1. Field of the Invention
The present invention relates to an image forming apparatus such as an MFP (Multi-Function Peripherals) as a digital compound machine, a copier or a printer. Besides, the invention relates to a photo sensor usable for an image forming apparatus or the like.
2. Description of the Related Art
Heretofore, an image forming apparatus such as an MFP includes a color printer unit having a photoconductive drum, a developing device, a transfer device and the like, and a sheet is transported to the color printer unit, and a color image is formed on the sheet.
Besides, the image forming apparatus includes plural detection means. For example, the transport of a sheet is detected so that the number of sheets is counted, or sheet clogging (jamming) in the middle of the transport or the like can be detected. Besides, in addition to the transport system, for example, in the color printer unit, the mounting of a toner cartridge is detected, or the rotation state of a rotation part is detected, and the operations of respective parts are controlled by using the detection result.
As the detection means, a photo sensor is widely used. The photo sensor includes a light emitting element and a light receiving element, a slit is provided in an optical path from the light emitting element to the light receiving element, and an object to be detected is made to pass through this slit, so that the presence/absence of the object to be detected is detected.
In a conventional photo sensor, since the thicknesses of the objects to be detected are different from each other, it is necessary to use the photo sensors suitable for the respective thicknesses, and when a space occupied by the photo sensors becomes large, it becomes difficult to arrange them in a limited space. Besides, since the photo sensors used are different in size and interval between terminals, when they are mounted on a printed board, it is necessary to design a print wiring circuit pattern according to the shapes of the photo sensors. Thus, in an apparatus using plural photo sensors different in kind, there is a defect that a print wiring pattern structure becomes complicated.
JP-A-6-104479 discloses a photo sensor including a light emitting element and a light receiving element. In this example, two light guides are disposed to be spaced from each other by a specified interval and to be opposite to each other, a light from the light emitting element is guided to the second light guide through the first light guide, and the light received by the second light guide is received by the light receiving element. Ends of the first and the second light guides are prism-shaped, an object to be detected is made to pass through between the first and the second light guides to shade the light, and the presence/absence of the object to be detected is detected.
However, in this example, the thickness of the object to be detected which is detected by the sensor is constant, and in the case where objects to be detected which are different in thickness or size are detected, it is necessary to prepare photo sensors different in the interval between the light emitting element and the light receiving element.
JP-A-2000-285278 discloses an example in which a sensor is used to monitor the transport of a sheet. In this example, it is an object to detect skewing of the sheet, a light emitting element and a light receiving element are arranged in parallel to the transport direction of the sheet, and the light from the light emitting element is refracted plural times by a reflecting mirror and is guided to the light receiving element. In the case where the sheet blocks the reflecting optical path, it is judged that the sheet skews.
Also in this example, there is no disclosure about a case where plural objects to be detected which are different in thickness or size are detected.
The invention provides a photo sensor in which even in the case where the thicknesses or sizes of objects to be detected are different from each other, an interval between a light emitting element and a light receiving element is constant. Besides, the invention provides an image forming apparatus using plural photo sensors.